Small particulate matter (with a diameter of 2.5
micrometers) reached a
reading of 1,000 in some parts of Harbin. More than 300 is
considered "hazardous," and the city has been forced to shut down
schools, airports, and buses because of the air.

The heavy smog is caused by industrial pollution, coal and
agricultural burning, and has been trapped by the mountains to
the west and wind patterns. The thick haze of smog is clearly
visible as the murky grey color in this true color VIIRS image
from the Suomi NPP satellite, taken on October 22, 2013 at 05:30
UTC.